Got basic webpage working. Need to make base page, static folders

2018-01-20 13:16:20 -08:00
parent 982037efc1
commit 1a375726ae
5625 changed files with 577078 additions and 0 deletions
@@ -0,0 +1,90 @@
+"""
+Synchronization primitives:
+
+    - reader-writer lock (preference to writers)
+
+(Contributed to Django by [email protected])
+"""
+
+import contextlib
+import threading
+
+
+class RWLock:
+    """
+    Classic implementation of reader-writer lock with preference to writers.
+
+    Readers can access a resource simultaneously.
+    Writers get an exclusive access.
+
+    API is self-descriptive:
+        reader_enters()
+        reader_leaves()
+        writer_enters()
+        writer_leaves()
+    """
+    def __init__(self):
+        self.mutex = threading.RLock()
+        self.can_read = threading.Semaphore(0)
+        self.can_write = threading.Semaphore(0)
+        self.active_readers = 0
+        self.active_writers = 0
+        self.waiting_readers = 0
+        self.waiting_writers = 0
+
+    def reader_enters(self):
+        with self.mutex:
+            if self.active_writers == 0 and self.waiting_writers == 0:
+                self.active_readers += 1
+                self.can_read.release()
+            else:
+                self.waiting_readers += 1
+        self.can_read.acquire()
+
+    def reader_leaves(self):
+        with self.mutex:
+            self.active_readers -= 1
+            if self.active_readers == 0 and self.waiting_writers != 0:
+                self.active_writers += 1
+                self.waiting_writers -= 1
+                self.can_write.release()
+
+    @contextlib.contextmanager
+    def reader(self):
+        self.reader_enters()
+        try:
+            yield
+        finally:
+            self.reader_leaves()
+
+    def writer_enters(self):
+        with self.mutex:
+            if self.active_writers == 0 and self.waiting_writers == 0 and self.active_readers == 0:
+                self.active_writers += 1
+                self.can_write.release()
+            else:
+                self.waiting_writers += 1
+        self.can_write.acquire()
+
+    def writer_leaves(self):
+        with self.mutex:
+            self.active_writers -= 1
+            if self.waiting_writers != 0:
+                self.active_writers += 1
+                self.waiting_writers -= 1
+                self.can_write.release()
+            elif self.waiting_readers != 0:
+                t = self.waiting_readers
+                self.waiting_readers = 0
+                self.active_readers += t
+                while t > 0:
+                    self.can_read.release()
+                    t -= 1
+
+    @contextlib.contextmanager
+    def writer(self):
+        self.writer_enters()
+        try:
+            yield
+        finally:
+            self.writer_leaves()